package com.clark.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.Iterator;
import java.util.NoSuchElementException;

import com.clark.func.Functions;

/**
 * An Iterator over the lines in a <code>Reader</code>.
 * <p>
 * <code>LineIterator</code> holds a reference to an open <code>Reader</code>.
 * When you have finished with the iterator you should close the reader to free
 * internal resources. This can be done by closing the reader directly, or by
 * calling the {@link #close()} or {@link #closeQuietly(LineIterator)} method on
 * the iterator.
 * <p>
 * The recommended usage pattern is:
 * 
 * <pre>
 * LineIterator it = FileUtils.lineIterator(file, &quot;UTF-8&quot;);
 * try {
 *     while (it.hasNext()) {
 *         String line = it.nextLine();
 *         // do something with line
 *     }
 * } finally {
 *     it.close();
 * }
 * </pre>
 * 
 * @author Niall Pemberton
 * @author Stephen Colebourne
 * @author Sandy McArthur
 * @version $Id: LineIterator.java 1022322 2010-10-13 23:20:42Z ggregory $
 * @since Commons IO 1.2
 */
public class LineIterator implements Iterator<String> {

    /** The reader that is being read. */
    private final BufferedReader bufferedReader;
    /** The current line. */
    private String cachedLine;
    /** A flag indicating if the iterator has been fully read. */
    private boolean finished = false;

    /**
     * Constructs an iterator of the lines for a <code>Reader</code>.
     * 
     * @param reader
     *            the <code>Reader</code> to read from, not null
     * @throws IllegalArgumentException
     *             if the reader is null
     */
    public LineIterator(final Reader reader) throws IllegalArgumentException {
        if (reader == null) {
            throw new IllegalArgumentException("Reader must not be null");
        }
        if (reader instanceof BufferedReader) {
            bufferedReader = (BufferedReader) reader;
        } else {
            bufferedReader = new BufferedReader(reader);
        }
    }

    // -----------------------------------------------------------------------
    /**
     * Indicates whether the <code>Reader</code> has more lines. If there is an
     * <code>IOException</code> then {@link #close()} will be called on this
     * instance.
     * 
     * @return <code>true</code> if the Reader has more lines
     * @throws IllegalStateException
     *             if an IO exception occurs
     */
    public boolean hasNext() {
        if (cachedLine != null) {
            return true;
        } else if (finished) {
            return false;
        } else {
            try {
                while (true) {
                    String line = bufferedReader.readLine();
                    if (line == null) {
                        finished = true;
                        return false;
                    } else if (isValidLine(line)) {
                        cachedLine = line;
                        return true;
                    }
                }
            } catch (IOException ioe) {
                close();
                throw new IllegalStateException(ioe);
            }
        }
    }

    /**
     * Overridable method to validate each line that is returned.
     * 
     * @param line
     *            the line that is to be validated
     * @return true if valid, false to remove from the iterator
     */
    protected boolean isValidLine(String line) {
        return true;
    }

    /**
     * Returns the next line in the wrapped <code>Reader</code>.
     * 
     * @return the next line from the input
     * @throws NoSuchElementException
     *             if there is no line to return
     */
    public String next() {
        return nextLine();
    }

    /**
     * Returns the next line in the wrapped <code>Reader</code>.
     * 
     * @return the next line from the input
     * @throws NoSuchElementException
     *             if there is no line to return
     */
    public String nextLine() {
        if (!hasNext()) {
            throw new NoSuchElementException("No more lines");
        }
        String currentLine = cachedLine;
        cachedLine = null;
        return currentLine;
    }

    /**
     * Closes the underlying <code>Reader</code> quietly. This method is useful
     * if you only want to process the first few lines of a larger file. If you
     * do not close the iterator then the <code>Reader</code> remains open. This
     * method can safely be called multiple times.
     */
    public void close() {
        finished = true;
        Functions.closeQuietly(bufferedReader);
        cachedLine = null;
    }

    /**
     * Unsupported.
     * 
     * @throws UnsupportedOperationException
     *             always
     */
    public void remove() {
        throw new UnsupportedOperationException(
                "Remove unsupported on LineIterator");
    }

    // -----------------------------------------------------------------------
    /**
     * Closes the iterator, handling null and ignoring exceptions.
     * 
     * @param iterator
     *            the iterator to close
     */
    public static void closeQuietly(LineIterator iterator) {
        if (iterator != null) {
            iterator.close();
        }
    }

}
